1. Field of the Invention
The present invention relates to a projection image display apparatus for magnifying and projecting an image on an imager onto a projection plane and, more particularly, is suitable for use in a projection image display apparatus that projects projection light onto a projection plane in an oblique direction.
2. Description of the Related Art
There have been commercialized and widely prevalent a projection image display apparatus (hereinafter referred to as “projector”) for magnifying and projecting an image on an imager (such as a liquid crystal panel) onto a projection plane (such as a screen). This kind of projector may cause a trapezoidal distortion in a projected image due to a discrepancy between a direction of an optical axis of a projection lens and a direction of a normal line to a projection plane. For correction of such a distortion, an installation state of a projector body may be adjusted such that the direction of the optical axis of the projection lens comes closer to the direction of the normal line to the projection plane, or an angle-adjustable reflecting mirror may be provided on a rear side of the projection lens so that an angle of the reflecting mirror can be adjusted so as to reduce the distortion. Alternatively, there is a method by which an image drawn on an imager is adjusted by signal processing. An image shaped so as to eliminate a distortion in advance is generated and drawn on the imager.
Although light from a projector is conventionally projected onto a screen in a front direction, there has recently been introduced a type of projector that projects projection light onto a screen in an oblique direction. By projecting projection light onto a screen from an oblique direction, this kind of projector reduces a possibility that the projection light is cut off by an obstacle such as a person and a shadow is cast on an image, as compared with image projection in a front direction. In addition, this kind of projector relieves a problem in that a person making a presentation near a screen suffers from the glare of light from the projector.
Such a trapezoidal distortion as described above becomes more pronounced when an incident angle of projection light is increased with respect to the normal line to a screen surface. Accordingly, when projection light is projected in an oblique direction as stated above, a trapezoidal distortion appears more prominently, as compared with the case where projection light is projected in a front direction.
In this case, although the trapezoidal distortion may be corrected by signal processing as stated above, there will occur a problem in that a resolution of the projected image deteriorates significantly. Further, in correcting the trapezoidal distortion by adjusting an installation state of the projector, only a slight change in the installation state greatly changes a position of a projected image, which causes a problem in that it is extremely difficult to let a projected image contained in a screen surface while correcting the trapezoidal distortion.
Moreover, in correcting the trapezoidal distortion by reflecting projection light by an angle-adjustable reflecting mirror, there will cause a problem in that the reflecting mirror needs to have a larger area as a tilting angle of projection light is increased with respect to the normal line to a screen plane, which leads to upsizing of the reflecting mirror. In this case, upsizing the reflecting mirror would cause a drive actuator in the reflecting mirror to be larger in size, resulting in the upsizing of the overall projector.